Drop-on-demand ink-jet and bubble-jet printers (collectively referred to as ink jet printers) propel fine ink droplets from nozzles onto a paper substrate adjacent the nozzle. Examples of these types of printers are the Cannon nozzles known as BCO1 and BCO2. By precisely controlling the trajectory and the time of ejection of the ink droplets, the ink jet nozzles print clear dots on paper. To achieve precise positioning of droplets of ink, ink jet nozzles must provide clear and clean orifices for the droplets to pass through as they fly from the nozzle to the surface of the paper. In a conventional drop-on-demand ink jet nozzle, there is an array of several orifices on the face of the nozzle from which the ink droplets are propelled. During printing, ink is ejected out of selected orifices in the array to form the desired images on the paper. The flight of the ink droplets and especially their impact on the paper surface creates a fine mist of ink that coats the surface of the nozzle. Also, during the ejection of the droplets, extraneous ink is sprayed and deposited on the nozzle face adjacent the orifices. This moist ink coating attracts paper fiber, dust, grit and other types of particles that can obstruct the nozzle orifices and block the ink droplets being sprayed from the nozzle. Also, the extraneous ink can build up such that it blocks the orifices. Accordingly, there is a need to regularly clean the nozzle plate of ink jet printers so that the array of orifices remains clear of ink and particles that would otherwise interfere with the printing of ink on the paper.
In the past, ink jet printers have been cleaned by wiper mechanisms that clean the nozzle plates and orifices. Between print jobs, the printer head moves away from the paper web to a cleaning station where is slides against a cleaning wiper. These wipers squeegee across the face of the nozzle plate and the openings of the orifices to remove particles that may be obstructing ink in the nozzles. Because the wipers themselves temporarily obstruct the nozzles, the wipers are used only when the ink jet printer is not printing. For example, a wiper may be positioned at the far edges of a carriage path, beyond the edges of the paper held adjacent the carriage path. An example of a wiping system is disclosed in U.S. Pat. No. 5,126,765, entitled "Ink Jet Recording Apparatus Having Cleaning Means For Cleaning A Recording Head".
Wipers have proven generally acceptable for desk top printing applications where each individual print job is relatively short and the times between when the print nozzles are wiped clean are relatively brief. In a typical desk-top ink-jet printer the carriage with the ink jet printing head can be shifted to a cleaning station after each print operation. Thus, in the usual desk top application, the printing nozzles are cleaned frequently by conventional wipers and tend not to clog with particles.
With continuous web-feed printing, the print nozzle is required to constantly print for many hours. This is unlike typical desk-top printing applications in which each printing operation is conducted in a relatively short period of time. Shifting the print head to a cleaning station away from the paper to be printed necessarily interrupts the printing operation of a continuous printer. While these interruptions do not substantially interfere with typical desk top print jobs, they do interfere with commercial printing of continuous webs. In this regard, conventional ink jet print heads have been found to require cleaning for every 30 to 60 minutes of continuous printing. Remote cleaning stations for ink jet printers are undesirable for commercial continuous printers because the print operation must be interrupted every one-half hour to one hour to clean the nozzles. Accordingly, there is a long-felt need for an apparatus and method for cleaning an ink jet nozzle without interrupting a print job.
Other prior art techniques for cleaning the nozzle face of an ink printer are to blow air at or around the ink nozzles to blow particles off the nozzle face or prevent particles from adhering to the nozzle face. Some of these techniques have included using ionized air to neutralize the static charges on dust particles that attract the dust to the nozzles. These techniques have achieved only partial success as is reported in U.S. Pat. No. 4,411,706, entitled "Method And Apparatus For Eliminating Dust From Ink Jet Printers." While blowing air at the nozzles can be accomplished as the nozzles are spraying ink, the turbulent air flow caused by the prior art blowers disrupts the trajectory of the ink droplets to the paper. Given that the prior systems for cleaning ink jet nozzles have been less than satisfactory, there has been a long felt-need for a technique for effectively cleaning the nozzles. That need was not fully satisfied until the current invention.
The current invention relates to a technique for cleaning an ink jet nozzle with a fluid, such as water or air, that flows across the face of the printing nozzle and entrains the dust and paper particles that adhere to the face of the nozzle. Once caught in the fluid, the particles are removed from the nozzles by the flow of the fluid.
In one embodiment of the invention a fluid stream flows across the face of the nozzle of an ink jet printer to clean the printer. This stream is located proximate to the nozzle array from which the ink droplets are propelled. Oust and paper particles that would otherwise clog the nozzle array are entrained in the fluid stream before they obstruct the orifices of the nozzle. A fluid source, drain supply fluid and network of fluid channels on the nozzle create a fluid stream path adapted to remove the particles and dust in the vicinity of the nozzle array. By continuously flowing fluid across the nozzle face, ink, grit and paper particles are continuously captured and removed from the nozzle array. In some embodiments, the fluid stream does not disrupt the projection of ink droplets from the nozzle array and, thus, does not interfere with printing.
In a first embodiment of the invention, the cleaning fluid is confined to channels adjacent the nozzle orifices. The orifices are not flushed with fluid. Accordingly, the ink jet nozzle can print while the cleaning fluid is flowing because the fluid flow does not obstruct or interfere with the ink droplets ejected from the nozzles to the paper. Accordingly, the first embodiment of the current invention provides a technique and apparatus for continually removing particles from an ink jet printer face while printing continues.
In a second embodiment of the invention, cleaning fluid flows directly over the print nozzle orifices to wash the orifices and nozzle in general. Printing is interrupted while the orifices are washed using the second embodiment. This orifice wash embodiment of the invention flushes out any ink residue, dust or paper fibers clogging the orifices. Thus, the second embodiment provides a more thorough cleaning of the print nozzle than does the first embodiment. The second embodiment of the invention may be used in conjunction with the first embodiment.
In a third embodiment of the invention, the array of nozzle orifices is shielded from ink spray and splatter by a nozzle plate. The nozzle plate is positioned in front of the orifices and includes a narrow slit through which ink droplets fly. The nozzle plate is separated by a small gap from the array of nozzle orifices and excess ink drains through this gap away from the nozzle orifices. This third embodiment may be used in conjunction with the first and second embodiments of the invention.
An object of the current invention is to clean the nozzle array of an ink jet printer and prevent ink, dirt and paper particles from obstructing the orifices of the nozzle array. It is a further object of the invention to continually capture and remove ink and particles from the nozzle array while the nozzles are printing and to wash the nozzles completely at other times. A further object of the invention is to extend the period of maintenance free printing for ink jet printers and to reduce the frequency of off-print cleaning occurrences required for ink jet printers. Moreover, another objective of the invention is to enhance the print quality of ink jet printers by overcoming many of the problems caused by extraneous, girt and paper particles that have clogged prior ink jet printers. These and other objectives are achieved by the invention that is shown and described in detail below.